Scalable switch matrix and demodulator bank architecture for a satellite uplink receiver

ABSTRACT

A scalable switch matrix and demodulator bank architecture for a satellite payload processor wherein the demodulators are connected to the output ports of the switches as the data load on the uplink beams varies. The switch matrix includes a first switch layer for receiving the uplink transmission beams and a plurality of demodulators connected to the output parts of the first switch layer. The number of demodulators is limited by the number of active uplink sub-bands which is generally less than the number of sub-bands per beam times the number of transmission beams. Thus, only a relatively few number of demodulators are distributed among the uplink transmission beams as required. This results in a readily scalable architecture having higher demodulation utilization rates than dedicated demodulation architectures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 09/732,955filed on Dec. 7, 2000 which was a continuation of U.S. patentapplication Ser. No. 09/369,069 filed on Aug. 5, 1999, now issued asU.S. Pat. No. 6,236,833 on May 22, 2001, the entire contents of whichare incorporated herein by this reference.

TECHNICAL FIELD

The present invention relates generally to switch matrices, and moreparticularly, to a scalable switch matrix and demodulator bankconfiguration for a high capacity multi-beam satellite uplink receiver.

BACKGROUND OF THE INVENTION

Generally, satellite uplink receivers are typically used to receive oneor more uplink transmission beams carrying radio frequency signals. Thereceivers demodulate the signals for further processing, and transmitthe data to downlink modulators for transmission on downlink beams. Sofar the satellites have been designed to process a relatively smallnumber of uplink transmission beams. As a result, satellite uplinkreceivers generally have dedicated demodulators for each potentialuplink transmission beam.

In order to increase the capacity and reuse the uplink spectrumfrequently and efficiently, there has been growing interest indeveloping satellites capable of processing several hundred uplinkbeams. Each beam can potentially carry traffic up to the capacity of thefull uplink spectrum. However, due to limitations on frequency re-useand satellite processing power, the total footprint capacity isgenerally much less than the maximum beam capacity times the number oftransmission beams. Accordingly, in a satellite system designed toprocess, for example, 400 uplink beams each having 12 sub-bands, 4800dedicated demodulators would be required. Because the maximum capacityis much less than the 4800 potential communication sub-bands, however,many demodulators would be underutilized and, even at maximum footprinttraffic, many demodulators would be idle.

As a result of low utilization rates, a dedicated demodulatorarchitecture has the drawbacks of relatively high power consumption andundesirable added weight to the satellite.

The traffic of a beam varies with the demand, time-of-day, and/or motionof the satellite (in the case of non-geosynchronous satellites). Thus,there exists a need for an uplink architecture with a pool ofdemodulators that can be assigned dynamically to the beams based ontheir needs. A scalable switch matrix provides reliable uplink signalprocessing, and reduces the amount of required hardware versus dedicateddemodulator architectures, thereby eliminating additional power, volume,mass, and complexity.

DISCLOSURE OF THE INVENTION

The present invention has several advantages over existingarchitectures. The present invention is a scalable switch matrix anddemodulator bank architecture for a satellite payload processor whereinthe demodulators are connected to the output ports of the switches andassigned optimally to the beams as the load on the uplink beams varies.Thus, a smaller number of demodulators are required to process theuplink signals. This results in a readily scalable architecture havinghigher utilization of the demodulators, smaller switch sizes, and ahigher efficiency and overall reliability.

These advantages are accomplished through the use of a high capacityswitch matrix for processing data from many uplink transmission beamswherein each of the transmission beams is capable of carrying an activecommunication signal in any one of several sub-bands.

The switch matrix includes a first switch layer including one or moreswitches, each having several inputs and outputs. Each of the switchinputs are connected to receive one of the uplink transmission beamssuch that the total number of switch inputs is greater than or equal tothe number of uplink input transmission beams. The switch matrix alsoincludes a plurality of demodulators for retrieving data from the activecommunication sub-bands of the transmission beams. The total number ofdemodulators is limited to the maximum number of communication sub-bandswhich can be active at any one given time. This number is generally muchless than the number of sub-bands per beam times the number of uplinktransmission beams.

A second switch layer is connected between the first switch layer andthe demodulators. The second switch layer includes groups of varyingnumbers of switches such that the output ports of the first switches areconnected to a varying number of demodulators. Thus, when a first switchreceives uplink transmission beams having many active communicationsub-bands, it routes the data traffic to an output port having acorresponding number of demodulators.

In another aspect of the invention, a tandem switch is configuredparallel to the first switch layer and is used to direct overflowtraffic to underutilized switches in the first switch layer. Thisarrangement of the switch matrix allows any of the uplink transmissionbeams to be connected to a time-varying number of demodulators. Otheradvantages of the invention will become apparent when viewed in light ofthe following detailed description and appended claims, and uponreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference shouldnow be had to the embodiments illustrated in greater detail in theaccompanying drawings and described below by way of examples of theinvention. In the drawings:

FIG. 1 is a schematic representation of a scalable switch matrix inaccordance with one embodiment of the present invention;

FIG. 1A is a table representing the input and output connectionsassociated with the first layer switches of FIG. 1; and

FIG. 2 is a schematic representation of a scalable switch matrixaccording to another embodiment of the present invention.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, there is shown one embodiment of the scalableswitch matrix and demodulator bank of the present invention. As shown inFIG. 1, the switch matrix includes a first switch layer 10, a secondswitch layer 12, and a plurality of demodulators 14. In this example,the switch matrix is configured to process a 400 beam uplink payloadwherein the uplink beams are divided into 200 left and 200 rightpolarizations. Only the first beam 16 and the last beam 18 are shown,although it is to be understood that uplink transmission beams 2 through199 would be similarly connected to the switch matrix.

Since one polarization is typically sufficient to carry the data load ofa majority of uplink transmissions, a plurality of 2 ×2 switches 20 anda 200 ×20 switch 22 are used to pick up the desired polarization for theload traffic cells, and direct both polarizations to the first switchlayer 10, if necessary, for uplink beams with heavy data traffic. Thus,there are 200 uplink transmission beams connected directly to the firstswitch layer 10 by the 2 ×2 switches 20, and as many as 20 additionaluplink transmission beams can be connected to the first switch layer 10by the 200 ×20 switch 22. This results in a total of 220 potential inputtransmission beams.

Alternatively, the 2 ×2 switches 20 and the 200 ×20 switch 22 could beeliminated and all of the uplink transmission beams could be directlyconnected to input ports of the switches within the first switch layer10 for a total of 400 potential input transmission beams.

The first switch layer 10 includes ten 28×28 switches 24 which, in thiscase, are point-to-point switches. In this example, ten 28×28 switches24 are shown because of the need to accommodate 220 inputs from the 2×2switches 20 and the 200×20 switch 22, as well as six inputs per switch24 received by the 60×60 tandem switch 26. Of course, any number ofswitches 24, including a single switch, could be used, and the size ofthe switch 24 could likewise be varied.

The tandem switch 26 is used to direct overflow traffic from switches 24operating at full capacity to other switches 24 operating at less thanfull capacity as is known in the act.

Since each input transmission beam requires a variable number ofdemodulators to process the data traffic associated with the input beam,the output ports of the 28×28 switches 24 are connected to a varyingnumber of 8×4 switches 28 in the second switch layer 12. The table inFIG. 1A shows the relationship between the number of output switch portsin the 28×28 switches 24 and the corresponding number of 8×4 switches 28that those output ports are connected to. As shown in FIG. 1A, the firstoutput port is connected to 12, 8×4 switches 28; the next two outputports are connected to 10, 8×4 switches 28; the next two output portsare connected to eight, 8×4 switches 28; and so on. By changing therelationship of the output ports and the connections in the secondswitch layer, the traffic pattern that the switches 24 of the firstswitch layer can support can be altered.

Referring again to FIG. 1, the maximum number of 8×4 switches 28connected to any single output port of the 28×28 switches 24 is 12which, in this example, corresponds to the number of frequency channelsor sub-bands associated with each uplink transmission beam.

The demodulators 14 connected to a particular 8×4 switch 28 are all ofthe same type and operate at the same frequency band. The demodulators14 connected to different 8×4 switches 28 of the same 28×28 switch 24operate at different frequency bands. The sum of these frequency bandscovers the entire allocated frequency spectrum which, in this case, isshown as 300 MHz. Once the demodulators 14 process the data received inthe uplink transmission beams, the data is passed to packet switch 30for routing the packets and then modulation and transmission on one ormore downlink beams (the downlink modulators and transmitter is notshown).

The total number of demodulators is a function of the maximum data ratefor the entire uplink footprint. Due to the satellite processing power,among other things, the total footprint traffic is generally much lessthan the maximum beam capacity times the number of uplink transmissionbeams. In the case of the switch shown in FIG. 1, the total number ofdemodulators is 480. This corresponds to four demodulators per sub-band,per input switch bank. This contrasts with the 4800 demodulators whichwould be required in a dedicated architecture for 400 transmission beamseach having 12 sub-bands. Here, the maximum data rate is defined as thetotal number of sub-bands in each transmission beam which could beactive at any one time.

All of the switches shown in FIG. 1 can receive and implement thecommands from a central processor (not shown) to connect any input portto any output port. The central processor is aware of the footprinttraffic and the active sub-bands within each beam.

The tandem switch 26 is used to distribute the load to other switches 24if the load on one or more of the 28×28 switches 24 exceeds thedemodulator availability at those switches. The central processordetermines which beams need to be off-loaded to other switches.

Referring to FIG. 2, there is shown a schematic diagram of anotherembodiment of the switch matrix of the present invention. In thisexample, again, the switch is intended to accommodate a 400 beam uplinkpayload having a 300 MHz spectrum divided into 12 frequency bands orsubchannels.

In this case, the first switch layer 40 includes 10 46×54 switches 42.Each of the switches 42 has 46 inputs—40 per switch to accommodate the400 uplink transmission beams, and six per switch to route overflow datatraffic to the tandem switch 26. Similarly, each switch 42 has 54outputs to accommodate four demodulators 44 per sub-band, and sixoutputs for overflow data traffic to the tandem switch 26.

Each demodulator 44 of a demodulator bank 46 is of the same type andoperates at the same frequency band. Each demodulator band 46 connectedto a different output port of the switches 42 and operates at adifferent frequency band. The sum of the frequency bands covers theentire allocated uplink frequency band spectrum, i.e. 300 MHz.

The switches 42 shown in FIG. 2, have broadcast or multi-cast capabilityas is known in the art. Thus, the switches 42 can multi-cast an inputbeam to any number of demodulators attached to the output ports asneeded to process the data traffic on the input transmission beam. Incontrast to the switches 24 of FIG. 1, switches 42 have increasedflexibility in adapting to various traffic patterns, but requireswitches with multi-cast capability and more cross-connections.

From the foregoing, it will be seen that there has been brought to theart a new and improved switch matrix architecture which overcomes thedrawbacks associated with dedicated demodulator architectures. While theinvention has been described in connection with one or more embodiments,it will be understood that the invention is not limited to thoseembodiments. On the contrary, the invention covers all alternatives,modifications, and equivalents, as may be included within the spirit andscope of the appended claims. For example, referring to FIG. 1, all ofthe switches 20, 22, 24, and 28 could be of a different number and sizedepending upon the number and characteristics of uplink beams andavailable technologies. Similarly, depending upon the uplink beampayload, the second switch layer 12 may be omitted (as in FIG. 2) or athird switch layer similar to the second may be required. Also, thedemodulators 14, 44 may be tunable demodulators rather than fixed at apredetermined frequency. It is, therefore, contemplated by the appendedclaims to cover any such modifications as incorporate those featureswhich constitute the essential features of these improvements within thetrue spirit and scope of the invention.

What is claimed is:
 1. A multibeam uplink switch matrix for a satellitecomprising: a first switch layer comprising at least onepoint-to-multipoint switch having a plurality of input and output portseach of said input ports connected to one wideband input transmission,beam of a plurality of input transmission beams and wherein the totalnumber of said input ports is greater than or equal to the plurality ofinput transmission beams; and a plurality of demodulator banks includingat least one demodulator, each of said demodulators being adapted todemodulate a sub-band from one of said wideband input transmissionbeams, at least one of each of said plurality of demodulator banksconnected to each of said output ports of said point-to-multipointswitch for receiving said wideband input transmission beam.
 2. Themultibeam uplink switch matrix of claim 1 wherein each of saiddemodulator banks operates at a predetermined frequency sub-band of saidinput transmission beams.
 3. The multibeam uplink switch matrix of claim1 wherein each of said demodulators is tunable.
 4. The multibeam uplinkswitch matrix of claim 1, further comprising a second switch layerincluding at least one switch connected between said first switch layerand said plurality of demodulator banks.
 5. The multibeam uplink switchmatrix of claim 4 wherein said second switch layer switch is apoint-to-point switch.
 6. The multibeam uplink switch matrix of claim 4wherein said second switch layer switch is a point-to-multipoint switch.